What is albedo and how to use it and how to prepare materials for games?
IMHO there is no single right or wrong way in how to prepare materials for games. Sometimes the engine dictates what you should prepare and often you just follow personal preferences.

Your project might also require different types of spec maps, for dry and rainy weather, for example. Cavity maps can produce all sorts of fancy effects like dirt, dust, worn edges, snow on top of rocks... 

I am a big fan of model recycling. Sometimes it's only a single part of a mesh, a fancy cycles material, but I also reuse complete models with textures. To get the necessary flexibility I bake huge textures and  separate maps - sometimes even for cavity. 

Albedo is basically the new diffuse ;-) Since many people started baking all kinds of effects into their diffuse maps it just seems to make sense to give the plain color without lights, ao, whatever a new name. Basically it's a "normalized" version of the "modern" diffuse map. 

Edit: You might watch Joel Burgess's GDC presentation about modular level design in Fallout 4. It's a great source of what can be achieved by reusing meshes with different material setups